Breaking up or not with long term partner

Me and my partner have been together 4 years and have a house and pets together.

I have doubted the relationship for a while now as it feels as though our spark and sexual chemistry has gone or dying out.

I love my partner so much but just can’t shake this feeling and seeing people happy and in love is killing me.

I feel so guilty because my partner doesn’t have a lot of friends and I feel they would be so lonely when we break up as their friends are my partners friends.

Also our pets, the thought of leaving them when they are like my own children is killing me they will think I’ve left them.

Our families get on so well and I’m so close to my partners family and the thought of them despising me is horrible.

We go on so many trips and do everything together I just don’t know what to do, I just don’t know if I can see us being engaged and married but yet the thought of them being with someone else kills e.

My heart and my head are tearing me apart and I feel the weight of the world is on my shoulders. I genuinely think my partner is amazing but I’m really not sure.

Sorry for the rant I have no one else to talk to.